1. Technical Field
The present invention relates to semiconductor devices, and more particularly, to semiconductor devices that output differential signals.
2. Related Art
Interface circuits for high speed transmission of low amplitude differential signals, such as Low Voltage Differential Signals (LVDS) have been conventionally used for a variety of electronic apparatuses. Such interface circuits are used for signal transmission between, for example, a main body of a notebook type personal computer (hereafter, referred to as a “PC”) and its liquid crystal display device. In addition, as the densification of various electronic equipment advances, interface circuits for high speed transmission of low amplitude differential signals are also used in substrates, for example, in substrates for liquid crystal displays. For example, there are so-called Mini-LVDS and Reduced Swing Differential Signaling (RSDS). The use of such low amplitude differential signals contributes to lower power consumption and lower Electro Magnetic Interference: electromagnetic interference (EMI) of various types of electrical equipment. RSDS is an interface standard for connecting between the liquid crystal controller and the driver IC. Two bias voltage signals to control the center voltage and the amplitude are inputted from a bias circuit to an RSDS output circuit. The RSDS output circuit outputs differential signals having an amplitude of a predetermined voltage width based on the two inputted bias signals with a predetermined center voltage as a reference (see, for example, Japanese Laid-open Patent Application 2002-314397).
Such an interface circuit is realized by a circuit formed on a semiconductor chip. Therefore, if forming regions of a plurality of transistors to be formed on the semiconductor substrate are far (distant) from one another, the operation characteristics of the transistors may vary, depending on the manufacturing process, for example, threshold voltages may vary, depending on the different locations of the forming regions of the transistors on the semiconductor substrate. For example, when an RSDS output circuit and a bias circuit are provided far from each other on a semiconductor chip, threshold values at which transistors turn on in response to a voltage given by the bias circuit may vary.
In the case of a differential signal, in particular, when the level of the center voltage of the differential signal to be outputted varies, a problem arises in that receiver side equipment that receives the differential signal cannot ensure the reception of the differential signal.
Accordingly, it is an object of the present invention to provide a semiconductor device that can set a center voltage level of a differential signal to a specified value.